1. Field of Use
This invention relates generally to protective control systems for preventing or stopping operation of equipment driven by internal combustion engines in the event of the existence or occurrence of fault conditions, such as low oil level, low oil pressure, high engine temperatures or the like.
In particular, it relates to such protective control systems which embody electric circuits including electric devices responsive to fault-sensing switches to control electrically operated actuators such as solenoid valves or the like.
2. Description of the Prior Art
Certain types of equipment, such as large water pumps which are driven by internal combustion engines to remove unwanted water from excavations and so forth, are intended to operate for relatively long periods of time while the human operator is not present and in many instances are under the supervision of persons who are not necessarily expert in the care, operation or maintenance of such engines. Accordingly, it is the practice to provide protective control systems for preventing start-up or running of the equipment if, for example, the oil level in the engine is too low or the engine is overheated from some unusual previous condition, and the human operator is unaware of these conditions. Such prior art protective systems also cause automatic shut-down of the equipment if low oil level, low oil pressure, high engine temperature or other undesirable fault conditions arise while the engine is running but unattended. Some prior art protective control systems embody electric circuits including electro-mechanical relays responsive to fault-sensing switches to operate switches which, in turn, actuate electrically operated actuators to shut off the engine. In some engines, these actuators take the form of solenoid valves which shut-off fuel flow to the engine. In other engines where fuel cut-off is a prohibited practice, these actuators take the form of a momentarily energizable solenoid operable to pull a latch which unlatches a flapper valve in the engine air intake and cuts off incoming air to the engine. Usually, provision is made to by-pass the protective control system to allow for start-up for limited engine operation. The heretofore-mentioned electro-mechanical relays and associated relay switches, since they embody movable components, are difficult to seal against entry of dirt, water and other contaminants, are prone to wear out because of repeated use and are also subject to vibrations which can cause accidental relay operations which shut down the equipment unnecessarily. In some cases, human operators even tamper with the relay (as, for example, inserting toothpicks to prevent motion of mechanical parts) to prevent unwarranted shutdowns, but these practices defeat the entire purpose of the protective control system. Some prior electro-mechanical relays also employ replaceable fuses which are inconvenient, time-consuming and costly to replace on the job site.